1. Field of the Invention
The invention relates to a ball valve for shutting off pipelines carrying liquid, gaseous and solids-laden media, particularly pipelines of large nominal diameter, the ball valve including a housing containing a ball having at least one bore therein and supported in a rotatable fashion in the housing by means of a spindle, and in which annular seals upstream and downstream of the ball in the direction of flow in the housing are provided for sealing off the inlet side of the ball from the outlet side when rotated to a closed position.
2. The Prior Art
Ball valves of this type are used as shut-off devices for liquid, gaseous and solids-laden media under pressure and under vacuum. The usual linear, circular passageway allows for the least possible flow resistance since the medium is carried in a smooth pipe. The sealing of the known ball valves is carried out by means of annular pistons, or often times, by means of sealing rings made of the most widely varied materials such as soft packings, ceramic, hard metal, etc.
These sealing rings are located in the housing immediately before (upstream of) and after (downstream of) the ball when viewed in the direction of flow. They seal the inlet side of the ball from the outlet side when the ball is in a shut-off position.
However, when the ball valve is opened, that is, when the ball is rotated by 90.degree. from the shut-off position by means of the spindle, the ball surface will temporarily lose sealing contact with the sealing rings. Since the ball cannot be supported within the housing without some play, there are dead spaces between the ball and the housing wall which clog up with medium, which will flow between the sealing ring and the opening cutout of the bore when the valve is switched, until finally it is no longer possible to open and close the valve.
Various suggestions have been made for minimizing the dead spaces. For example, the dead spaces can be filled during the assembly of the ball into the housing. In order for the valve to be able to work reliably, a certain gap must still remain between the ball and the filling material, and as a result, this gap can still clog up.
Furthermore, material forces its way from the dead spaces into the area between the spindle and the housing. Since the flow materials can be abrasive or sticky, or even materials which crystallize, it can be foreseen when an actuating of the spindle will become impossible.
In addition, particularly in the case of ball valves with large nominal diameters and in the case of high pressures, it is necessary to support the heavy ball with a step bearing. With the known ball bearings, the medium also gets into this region and clogs it.
It is therefore the object of the invention to configure a ball valve of the type described wherein penetration of medium into the dead spaces, and from there into the area of the spindle or a step bearing, is prevented right from the very start in order to increase the service life of the valve, as well as its operational reliability.